Congolese army soldiers guard the main road north from Goma, the capital of North Kivu province. Photograph: Joe Bavier/Reuters

Peace accords that were to put an end to the conflicts that killed millions in the Democratic Republic of Congo are collapsing after a powerful renegade Tutsi general declared war on the government.

The United Nations has started airlifting thousands of government troops into the eastern Kivu region, which has endured two foreign invasions and more than a decade of civil war. About 4 million people have died in the conflicts.

Fighting has renewed after General Laurent Nkunda pulled thousands of his men out of the national army last week, just months after they were integrated under the peace accords, and began attacking government troops whom he accused of collaborating with Hutu forces that fled into Congo after carrying out the 1994 genocide of Tutsis in Rwanda.

Gen Nkunda says he has gone back to war to protect the hundreds of thousands of Tutsis who live in the Kivu region and are still targeted by Hutu rebels. But the UN peacekeeping force in Congo has thrown its support behind the government's claim that Gen Nkunda is a "bandit", raising the prospect of another major conflict.

UN helicopters left Goma in relays carrying government soldiers to Masisi, where the army is under siege from a much larger and better trained force under Gen Nkunda. Scores of men have been killed.

Gen Nkunda told the BBC's Africa service that his forces captured members of the 7,000 strong FDLR - the Rwandan Hutu extremist rebel group who have been killing Tutsis in the region - and handed them over to the UN. "For me it's a state of war ... we have prisoners of war from the FDLR who were attacking with the government troops," he said.

Congo's defence minister, Tshikez Djemu, said that if Gen Nkunda does not lay down his arms he and his army will be considered bandits and attacked.

Thousands of civilians fled their homes in Masisi and from towns such as Rutshuru, where Gen Nkunda has much of his 8,000-strong army. Soldiers at his local headquarters in Rutshuru had stripped off their government uniforms and changed into outfits similar to the Rwandan army's. Some spoke English not French, suggesting they are Tutsis of Rwandan origin, raised in exile in Uganda or Tanzania.

The UN accuses Gen Nkunda's forces of killings and rapes in fighting with the FDLR that has driven up to 200,000 people from their homes in recent months, according to the World Food Programme.

Rwanda's foreign minister, Charles Murigande, is expected in the Congolese capital Kinshasa today for a rare high-level meeting between the two countries, which continue to have tense relations after two Rwandan invasions.

Mr Murigande denies Congolese claims that Rwanda is secretly backing Gen Nkunda but says he understands the general's fears for the safety of the Tutsis in Kivu after the Congolese government halted a military offensive against the Hutu rebels, including members of the Interahamwe which led the killing in the Rwandan genocide.

"These ex-Interahamwe have been looting, maiming, raping, killing the Congolese people in the hope that they will gather enough strength to come to Rwanda and finish a genocide they were unable to finish in 1994," he told the BBC African service. "I would not imagine that a serious government can contemplate living with people who are responsible for such horrible crimes."

Rwanda has demanded that Congo crush the FDLR and has offered to send troops to help but Kinshasa suspects that they would be used to further entrench Kigali's influence over the region.

A diplomatic source told the Guardian that while the UN views Gen Nkunda as a destabilising influence, there will be no end to the conflict without also dealing with the FDLR and addressing Rwandan security concerns.

"They can't go after Nkunda without dealing with the FDLR," he said. "Rwanda won't allow the FDLR to remain on the border but the [Congolese] army seems incapable of dealing with them. That's why Nkunda exists and why the Rwandans support him."

Backstory

The roots of the conflict lie in the 1994 genocide in Rwanda. The Hutu extremists who killed 800,000 Tutsis fled into what was then Zaire and launched attacks on Rwanda's Tutsi rebel government. Rwanda invaded twice to attack the Hutu insurgents but the conflict ended with the east of Congo controlled by rebels backed by Rwanda and Uganda. Peace accords and elections last year offered hope but resolution is likely only if Rwanda no longer feels its border is threatened by Hutu rebels.